#root {
  width: 800px;
  margin: 0 auto;
}
#root .header {
  height: 100px;
  background: #cef;
}
#root .header:hover {
  background: #c90;
}
@media screen and (min-width: 700px) and (max-width: 800px) {
  #root .header {
    background: #254b5e;
  }
}
@media screen and (min-width: 800px) and (max-width: 900px) {
  #root .header {
    background: #53a723;
  }
}
#root > .content {
  height: 500px;
  padding-top: 50px;
}
#root > .content > .left {
  width: 150px;
  height: 200px;
  background: #c89;
  float: left;
}
#root > .content > .right {
  width: 600px;
  height: 400px;
  background: #89c;
  float: right;
}
#root > .content::after {
  content: '';
  display: block;
  clear: both;
}
